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Gen 2 Alternator question

rizzo

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I have read most of the posts. My gen 2 light is not coming on. I can get it to come on when I touch the electrical tester to the plug on the alternator. I think the alternator must be bad. I had it tested and the guy said when he excited the 2nd plug (farthest from the + terminal) the alternator worked. Could there be something wrong in the regulator that is not letting the plug 1 work? everything elso on the truck checks out. ie: bulb, relay diode, fuses.
 

Warthog

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Plug the two pin plug at the alternator. Check the voltage on the red and brown wires. You should get these readings

key off:
red wire - 24v
brown wire - 0v

key in run position:
red wire - 24v
brown wire - 24v

Make sure the plug and the two terminals are clean
 

rizzo

Active member
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Location
Port Huron, MI
plug the two pin plug at the alternator. Check the voltage on the red and brown wires. You should get these readings

key off:
red wire - 24v
brown wire - 0v

key in run position:
red wire - 24v
brown wire - 24v

Make sure the plug and the two terminals are clean
Those are the voltages I get. I think the problem is in the alternator. I tested the triple diode and got two different ohm readings. I tested the rectifier bridge by using + terminal and - terminal and only had a reading in one direction. The alternator has low miles, but a few years on a rebuild. I'm wondering if I should just replace the regulator.
 
Last edited:

Warthog

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Time to take the unit apart. More than likely it is the voltage regulator.
 

Warthog

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http://www.aspwholesale.com/index.php?act=viewProd&productId=1650
http://www.aspwholesale.com/index.php?act=viewProd&productId=987
http://www.aspwholesale.com/index.php?act=viewProd&productId=184

http://www.aspwholesale.com/index.php?act=viewProd&productId=5137

Sound like the rectifier is okay. I would replace the voltage regulator and the diode trio. The prices are too cheap not to.

The TM 9-2320-289-34P has the GM part numbers for the alternator items. A local parts store (NAPA?) should be able to cross reference them.

Voltage Regulator
GM - 1116423
NAPA - ECH VR148
 
Last edited:

rizzo

Active member
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Location
Port Huron, MI
I fixed it. Autozone has an tester that checks the rectifier and the voltage regulator. and it checked out there and another place.

I called a friend over and told him how everything seems to work but my dash light is not working. but it does work when it is grounded by the light tester. The first thing he did was start to check continuity from the wires at the alternator to the battery. The 12v wire hooked up the the negative ground showed a massive resistance. We checked different sections of the circuit and found the resistance to be in the 12v terminal on the firewall. I added star washers to all the eyelets on the terminal and it was fixed. (I buy star washers in bulk for all my electrical connections)

Reading Warthogs post about connections I did change the white exciter plug to the alternator and I added star washers to the other connections on the alternator. I had also cleaned all the connections on the instrument panel and bought a new relay. I had read a post about cleaning the terminals on the firewall, but did not act on it because:
1) The outer eyelets were clean and looked brand new (shame on me for not checking underneath. I had fixed those connections at a time before I put star washers on everything.)
2) Knowing that it was some sort of ground problem, I was not realizing that the 12v hooked to isolated ground on the alternator is actually the ground even though it is 12v. It makes perfect sense now.

I asked my friend if there is any indicator that there might be resistance/connection problem and he said that other than load testing the wire, sometimes it will show reduced voltage. I remembered when I was checking all my voltages I was getting a reduced reading on the 12v isolated ground wire. I have learned a valuable lesson.

This was an odd problem because every wire had the right voltage and checked out ok with light tester. I hope this post helps someone in the future.

Thanks to everyone.
 

scottladdy

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Location
CT
Suggest you add a dab of dielectric grease to each of your cleaned up connections as well. Really helps reduce the oxidation of these connections.
 

doghead

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Great info, Thanks for the update.

Glad you got it figured out.
 
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